Bomb sight



v e Z0, 1939. E. w. CHAFEE ET A1.

BOMB SIGHT Original Filed Feb. 20, 1936 3 Shee='f.s-Sheel'4 2 E, W. CHAFEE ET AL BOMB SIGHT 3 sheets-Sheet 3 Original Filed Feb. 20, 1956 Van linken, Sperry @yr-coco orr, I. Y., sind Howard N. 5., assigner?, to Eric., Erooidyn,

Application 29, 1%33, No. 64,254@ .Rene-wee Marcil Ll, w3c

12 Cieiois.

This invention relates to bomb sights for eircreft which ere designed to direct the course of the aircraft so that its ground 'crock (neglecting oiset) posses through the target in e straight line and which determine the exact point et which the bombs shall be released to strike the target. More specifically, this invention .constitutes an improvement or simplification of the type o bomb sicht disclosed inthe prior joint application oi Earl W. Choice, one of the joint inventors herein, end Hugh. Iurtsgn, Serial 'o. GBJEEG, flied June 18, M332; By the present invention, the number of hond settings in the sight is reduced end the computing mechanism slmplled.

Referring to the drawings showing one form our invention may assume,

ig. 'l vis o. diagram of the computing portion of the sight, showing the sight itself dzigremmatcolly.

Fig. 2 is side View, partly iii section, of e: portion of the sieht, showing the eyro vertical the opi/ioni sjrstem.

Fig. 3 is e detailed sectional View of the mounting for the of sight pris l.

Fie. is pien View of the eltitude indicctor driven by the variable speed motor.

Fig. 5 is en elevation diagram showing the theory of operation of the sieht.

5 is e pien View of the vectors involved in cross wind bombing.

Bomb sights may be cozisidewd es mede up of several units, nemely, the ootlcel unit ood the computing unit, oli contained within the common casing i. rEhe optical system' comprises, iii general, o, telescope ai: roteteoly mounted in the top of casing i which, through an optic-el upon the target on 'the ground es the aircraft.

approaches and iies over the some, the prism rotating, of course, et heli the angular rote of the line of sight. Seid prism is also preferably mounted for timing about e fore et axis on the craft so that the proper offset angie moy be set up, otter the marmer disclosed in the prior potent'to Mortimer No.

1,783,759, dated December 2. 193C, on Eomb ccv'ni: Q,-..

As shown, thc pivotal transverse shoft which the mirror is mounted, is journaled in e ring lo which, in turn, is promoted or angular onl (Ci. Elie-4&5)

adjustment in an outer fixed guide H. The adjustment of the prism about the transverse exis to follow the target is shown as effected through o. rod i2 having o, swivel connection l2 with the beck frame il' of the prism, the boil and socket being held together oy spring The adjustment shout the longitudinal axis for the offset ongle or deflection is shown es effected through an erm 53 secured to the hack of ring lil. The line of sight from the ground enters through the window l (Fig. 2) and is rclectecl by the prism to e second fixed prism l which rlirects the along a vertical line through the objective lenses iS which focus 'the image on the stabilized reticolo El. v

Preferably, we ocorporete in the sight o moans for quickly and accurately determining the cor rect drift angle. For this purpose We have shown om euxiiiery drift prism il' or other double reflcctor slidobiy' mounted between the prism is? and the lenses i6. Seid drift orism is normally of this line of sl, y hoodie iii, pivotcd et eno having teeth 2.' thereon meshing with reci: teeth ifs the framework carrying the prism, which is slid obli? moiinted on tiociwey 'ilfoen it is sirerl to escerteto the drift, however, the hoodie i3 is moved to the position shown in dotted line: in Fig. 2, pushing the prism i? to the left into the full line position, whereby, by double rc t ection, the image ci ground iyng vertically below the craft, es seco through the window ii', is reiiccted. up through the lenses i8 to the reticolo. The bomber, in looking through the telescope, then sees objects on the ground pessime; across the optical field. As the motion oi' these objects in relation to the reticole is caused only by the forward motion of the cisne' over the earth, the rol? and pitch oi' the piene being token out by the stabilized reticolo, the direction oli' motion across the field is parallel to the ground course the plone is flying. ',hereorc, the sight os e, whole is turned until the objects in the field of View move cloni; or parallel to the fore and oft hair on the vretlcule, theo the sight `will be pointed in the direction nl' the ground course or, in other words, the correct drift angle for thet particular course will be set into the como sight. After obteinirie' t'c correct drift ed the prism is moved C' t handle i3 to the left lo 2.

of the wey momie position there it i o the field of View. I s

r1, ...,m A h. his eye from the romero e of through the telescope, l may sec citi el; um ,elfhvw +Mw-n1:- m- Hm url-mm", l'ov'potifg H15 ple-ne at will or ei'most slrriullaneousiy,

The zoem-'ly ground speed is set up thro-:gh hemlie E5, by which 2.11 automatic means is set in actuel opere- 4The gyresoopc l is sii-oon :as zfzountcd .for oseil lei-ion about transverse 2; in cuter gluibeil riiie; i5 which, iii turn, mounted for oscillotion u ore and oit on trunnions 2--P.C in fixed. frame Si. Said girnbal is provided with forwardly extending arms which support the frame 3G on transverse axis so that. e common gimbal is provided for both the gyroscoie and reticule freine. The gyroseoue is preferably locked until the sight is thrown into operation, by means of loci; e' or caging fingere Afl-'i' pivoted around the base thereof, all. es more fully disclosed in the aforesaid prior application.

Referring now to tue commuting mechanism.,

i the prism E is rotated about arie to lreep the crease Witli increased altitude.

target in view, by means of e oar shown as mounted on a shaft and. driving; the prism through gearing Si, shaft El', erm 38 and the aforesaid linl l2. If the prism, ie turned et such e rate ae to keep the line or" sight on the target,

this rete may be used as one o the known factors in solving' for the desired point or release o the bomb, sometimes termed the ronge angle. Prei- .erably the angular movement ci the erm lii is resolved into a horizontal component representing ground speed (GS). To tlus end, the bar is shown proviff-ci with o slot into which s e piu. r f on o. nut Si threaded on scrceT :utc of turn ci scr-evi shaft, therefore, is e.. function oi the ground speed, but also inverte function of altitude since the speed oi movement of the prism will de- 'f tbe niechanism is laid out for one particule-r altitude, say 5G56 reet, the introduction oi' any other altitude could be compensated for by multiplying by the retio ci' the chosen altitude l to the actuel ultitude H. the retto being known es the altitude ratio. Hoving the speed of shaft 2 proportional to ground speed and the altitude ratio, we combine the same with the time of fell of tbe berno in, order to obtain. the wlioie ronge to the seele ci the instrument, i.- e., having regard. to the altitude ratio, which ronge we term herein Rm.. Since the Whole range (Re) is equal to tlie'time of fall of the bomb (T) times tlie ground sneed (GS) i. e.,

Rw: TX GS it follows that Rea (whole renee to seele of the instrument) H TX GSX which may also be Written 'fue time ci fell of tire bomb (T),` however, varies with altitude H' and with the terminal velocity Tv or the particular bomb employed, both o which quantities E' and Tv are known. We

therefore provide a. mechanical integrator to solve tbc above equation from the known factors. We drive a. Variable speed disc 5l et u speed reuresenting or, in other Words, inversely proportional to eltitude and terminal velocity. This may be ciiecteci by driving Elie some from a. variable speed motor Eil through. suitable gearing, the speed of the motor being accurately controlled by any suitable form of speed governor El from a. hand setting nieonslii. As shown, the ily ball governor is driven from the motor shaft through` HE and makes and breaks a Contact i il on lever i i2, the position oi which is varied by rotating thumb piece to turn screw H3. Said Contact serves to out e resistance i (Il in and out of the armature circu'v Eil to regulate the motor speed. The motor also drives a speedometer pointer E reedoble upon dial 5S which. is graduated. :it (see Fig. inversely in altitude instead of R. P. The altitude dial, however, is adjustable in acm cordance with the terminal velocity of the bomb employed by means of e. setting lrnob 9- wliieli is turned to adinet the arbitrary scale ill graduated in terminal velocity of the horribwitli reference to a fixed index t". The terminal. velocity ci the bomb is of couree dependent upon the bombs specific gravity, shape, ete., and it is lien-ce frequently referred to as the bomb characteristics. Therefore, by setting up'rst the proper terminal velocity for the type of bomb employed and i'izen adjusting tbe variable sneed knob until the speed @meter pointer Eli' indicates or matches known altitude, the disc 5i will be driven at e sneed proportional to The driven cylinder of the variable speed geur must be driven at a speed proportional to the ground speed multiplied by the altitude ratio it' the sight is kept on the target, so that the mechanism, in dividing this product by solves the above equation for Therefore the linear position of the bull or other type roller from the center of the disc represents the total range or Rw. This is set in by turning the knob on the threaded sllet Qt on which the nui, lil is threaded, which carries tbe ball Efe, soie. luie-l:V operating as a ground speed sync ionizingV knob. Shaft is shown as driven from cylinder t3 through cross shaft S5 and geaing tl d For hand setting, a. knob ll is shown, having a two speed gear cozuiection itil with. siiet From the diagram in Fig. 5 it is apparent that the true range It is equal to the whole range Re minus trail Y. Tl'lereore it is necessary to snip tract the trail from the Whole range in positioning' the range arm 'Fue trail valueis introduced from the shaft lt' that is connected to one arm of a direrential 'l l, the other being connected to and driven irorn the shaft The resulting dierence rotates e. disc l2 on which e, release angle seele may' be inscribed, and also rotates the renee angie bar or erm carrying releose contact cooperating with e release Contact it on the continuously driven disc l5, which may be provided with e scale 'i6 showing the present sight angle. disc is shown driven directly from the screw shaft i2 which, it will be reinembered, is rotated proportionally to TraitY mechanism If a bomb were dropped from an airplane in vacuo, it would remain directly under the plane. However, when dropped through air, the bomb is retarded by the air resistance so that to an observer in the plane it trails behind the airplane a distance BD, where D is ground projection of the airplanes position C at the instant of impact with the ground. This distance is termed the trail Y. For a given altitude, the trail is a function of air speed (AS) and the terminal velocity of the bomb (Tv).

fAS IT.,

According to our present invention, the trail as an angular quantity is obtained in a simple manner by employing a cylindrical scale il on which curves 77' marked in air speed are plotted with the circumferential distances proportional to the proper function of terminal velocity and the axial distances equalto trail, the curves being plotted from experimental data. The cylinder is rotated from the terminal Velocity or bomb characteristics setting knob Gil on Tv scale ffii. Co operating with curves 'iT-is a movable pointer 78, the hub of which is threaded on shaft '16, turned from the air speed setting knob When the pointer is set on the proper air speed curve as shown on the scale, the shaft 'luis rotated to an angular distance representing trail, which is subtracted from the whole range, as explained above.

Oiset mechanism In case cross wind is blowing, an additional factor must also be interposed (see Fig. 6). In this diagram the vector AS represents true air speed in magnitude and direction and the vector W the speed and direction of the wind. The ground speed of the craft would therefore be represented by the vector AD. If a bomb is released at O, however, it will not fall on the ground speed line, but will fall down wind to one side of the ground speed line, namely, at point B, the perpendicular distance BB from B to OD being termed the offset. As shown in the above figure, the oiset is equal to the trail Y multiplied by sin ci, and it will also beseen that the ange d is equal to the known drift angle. It is therefore necessary to determine the olset angie, in other words, the angle through which the prism S must be turned. about the fore and aft axis within its mounting il so that the alr craft will ily to one side of the true ground course a distance equal to BB. Such angle is a uncton of BB and altitude and since E' is set into the machine as an operating ratio, the offset angle is a function of the oiiset.

The olset mechanism is shown as having the trail fed into the same from the shalt it through gearing 8l which turns shaft BS, and. the drift angle is automatically set into the device from the turning of the sight around its vertical axis from the fore and aft line to a line which is perallel to the ground course, as previously described.

' about the axis or shaft 88.

This is represented as eected, in the diagram, through the azimuth control knob B2 which turns the shaft 83 through gearing 85. Said shaft is shown as having a pinion 35 meshing with a large internal gear Sii on the base of the sight, as more completely described in the prior application of Earl W. Chafee, one of the joint inventors herein, and Hugh lii'urtegh, Serial No. 618,080, iled June 18, 1932, for Bomb sight. Shaft 83 at the same time turns the bracket Bl Said bracket rotate ably supports, in two arms SQ thereof', a threaded shaft Sil which is rotated through bevel gears 9i from the shaft 88. A nut S22 is threaded on said shaft, which carries pin 93 engaging in a vertical slot 94 in a slide 95. Said slide will therefore be moved laterally a distance proportional to Yxsin d, representing the oiset distance, which, as explained, is proportional to the oiset since the altitude ratio aiects the whole machine. The lateral movement of said slide S35 rocks the lever I3 to rotate the prism mounting i@ within the housing ll so as to give the prism the proper odset angle to offset the line of sight the proper amount. l Y

Operation in brief, Athe operation of our invention is as follows. Before taking oi', the proper terminal velocity or bomb characteristics settings may be put in by the knobs Sii and Gil. After the target is sighted, the drift angle ls set up as explained, by turning the knob 82, and this automatically sets in the proper ofset angle to the prism il. As soon as a straight ground track from the target is arrived at, the complete mechanism is set in operation, the knob being adjusted so that the pointer reads the known altitude on the dial Eil, the itnob being adjusted until the liao of sight is maintained continuously on the target. The indicated air speed is set up by turning knob 8B to position pointer lil on the scale l. The mechanism will then automatically set the rangev bar 68 in the proper position to release the bomb by energizing solenoid H5 when the release disc "lil, which is continuously rotated from the shaft |32, brings the release contact ifi under 1E. If desired, an additional warning Contact 9G' may be provided to flash a signal l i5 when the range angle is being approached.

As many changes could be made in the'above construction and many apparently widely differ ent embodiments of this invention could he made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a' limiting sense.

Having described our invention, what We claim and desire to secure by letters Patent is:

l. In a bomb sight, a variable speed device for maintaining the line of sight on the target, comprising a revoluble disc, a roller driven thereby, means for radially adjusting the roller on the disc, means for rotating the line of sight from said roller, and means for varying the speed of said disc inversely in accordance with altitude, whereby range is indicated directly by the radial position of roller.

0. *n bomb sight for aircraft, a t

for rotating the line of sight .rthe same on the target, a speedometer driven by r graduated in terms of thc reciprocal of the altitude, and means for controlling they come 'Te 3. A bomb sight as claimed in claim 2, wherein the scale o said speedometer is adjustable in accordance with bomb characteristics, whereby the altitude setting is altered for dillercnt types of bombs.

4. In a bomb sight, means providing an angularly movable line of sight, a three part integrating device for deriving the range angle or total range as a xed quantity, means for driving one of said parts at a speed inversely proportional to the time of fall of the bomb and means for setting a second part driven by said rst part' so that the third part driven by said second part keeps the line of sight on the target, Wliereby the speed oi the third part is a whereby the set position of the second part represents Whole range.

5. A trail computing device for bomb sights, comprising a cylinder having axially spaced curves laid out thereon marked in air speed (AS) a. circular scale on said cylinder graduated in bomb characteristics, a setting knob rotating said scale to the proper bomb characteristic setting, an index adjustable axially along said cylinder, and means for axially adjusting said index to intersect the proper air speed curve, whereby the axial position thereof represents the trail angle when the cylinder has been rotated to the proper bomb characteristic reading and said index intersects the proper air speed curve.

6. In a bomb sight for aircraft, a. variable speed drive for maintaining the line of sight on the target, including a primary driving member, a driven member for turning the line of sight, and an intermediate adjustable member which drives the driven member from the primary driving', member, means for varying the speed oi the driving member inversely proportional to the time of fall of the bomb, and manual means for adjusting the position of said intermediate member to actuate the driven member at a speed to maintain the line of sight on the target.

'7. A bomb sight as claimed in claim 6, wherein the position of the intermediate member determines the range angle or whole range.

8. In a bomb sight, means for determining whole 'range (Rm) with respect to the altitude ratio which is employed as the present scale of the instrument, means for determining trail (Y) as an Vfunction of GS aieaeee angular quantity, means for determining the oiiset angle, and means for combining said'trail angle directly with said Whole range (Rw.) to give true range angle and for simultaneously introducing said trail angle into said offset determining means.'

9. In a bomb sight for aircraft, means for rotating the line of sight to keep the same on a target, including a member rotatable about a center for rotating the line of sight, av rectilinearly movable member for rotating said rotatable member, whereby the rate of movement thereof equals ground speed (GS) with respect to the or instantaneous scale of the machine, a variable speed gear for moving said rectilinearly movable member, said gear including a disc driven at a speed proportional. to a function of the time of fall of the bomb, and a roller carriage radially positioned thereon to keep the sight on the target, whereby the radial position of said roller carriage on said disc is proportional to the whole range (Rwa) with respect to said instantaneous scale oi' the machine.

l0, In a bomb sight, a A'variable speed device for turning the line of sight to maintain the same on the target, 'including a variable speed motor, a variable speed drive actuated thereby for turning the sight, a speedometer driven by said motor, means for governing the speed of said motor to maintain the speedometer indications at a value bearing a predetermined relationship to altitude, and independent means for adjusting said variable speed drive to keep the sight on the target.

il. A. sight for aircraft. as claimed 1n claim l0, in which said speedometer is graduated in inverse altitude and is also adjustable according to the bomb characteristics.

12. A trail computing device for bomb sights, comprising a cylinder having axially spaced curves laid out thereon marked in air speed (AS). a circular scale on said cylinder graduated in bomb characteristics, a setting knob rotating said scale to the proper bomb characteristic setting, an index adjustable axially along said cylinder, means for axially adjusting said index to intersect the proper air speed curve, whereby the axial position thereof represents the trail angle when the cylinder has been rotated to the proper bomb characteristic reading and said index intersects the proper air speed curve, and an oiisct mechanism for said sight means for introducing the trail angle so obtained directly into said ofset mechanism.

EARL W. CHAFEE. HOWARD C. VAN AUKEN. 

